Light emitting diode and fabrication method thereof

ABSTRACT

A light emitting diode (LED) and a method for fabricating the same, capable of improving brightness by forming a InGaN layer having a low concentration of indium, and whose lattice constant is similar to that of an active layer of the LED, is provided. The LED includes: a buffer layer disposed on a sapphire substrate; a GaN layer disposed on the buffer layer; a doped GaN layer disposed on the GaN layer; a GaN layer having indium disposed on the GaN layer; an active layer disposed on the GaN layer having indium; and a P-type GaN disposed on the active layer. Here, an empirical formula of the GaN layer having indium is given by In(x)Ga(1-x)N and a range of x is given by 0&lt;x&lt;2, and a thickness of the GaN layer having indium is 50-200 Å.

This application is a Divisional of co-pending application Ser. No.11/333,247 filed on Jan. 18, 2006, and for which priority is claimedunder 35 U.S.C. § 120; and this application claims priority ofApplication No. 2003/48993 filed in Korea on Jul. 18, 2003 under 35U.S.C. § 119; the entire contents of all are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to a light emitting diode, and moreparticularly, to a light emitting diode and a fabrication method thereofin which a light efficiency can be improved by forming a layercontaining indium (In), whose lattice constant is similar to that of anactive layer formed in the LED.

BACKGROUND ART

Generally, a light emitting diode (LED) is a kind of semiconductordevice, and it converts an electrical signal into infrared ray or lightby using a characteristic of a compound semiconductor, to send orreceive a signal. The LED is used for home appliances, a remotecontroller, an electronic display board, a display device, a variety ofautomation apparatuses and the like.

An operation principle of the LED will be briefly described in thefollowing.

When a forward voltage is applied to a semiconductor of a specificchemical element, electrons and holes are recombined with each otherwhile moving through a positive-negative junction. The recombination ofthe electrons and the holes causes an energy level to fall down, so thatlight is emitted.

The LED is generally manufactured to have a very small size of 0.25 mm²and is mounted on a printed circuit board (PCB) or a lead frame using anepoxy mold.

Representative of the LEDs is a plastic package of 5 mm (T 1 ¾) or a newpackage being developed in a specific application field.

A color of light emitted from the LED is determined by a wavelengthobtained depending on a combination of elements constituting asemiconductor chip.

Particularly, as an information communication apparatus is in a trend ofa small-size and slimness, the communication apparatus has moreminiaturized parts such as a resistance, a condenser, and a noisefilter. The LED is manufactured in a form of a surface mounted device(hereinafter, referred to as “SMD”) so as to be directly mounted on aprinted circuit board (hereinafter, referred to as “PCB”).

Accordingly, an LED lamp for a display device is being developed in theform of the SMD. Such an SMD can substitute a related-art simple lamp.The SMD is used for a lamp display, a character display, an imagedisplay and the like that express various colors.

Further, as a high-density integration technology for a semiconductordevice is developed and a consumer prefers a more compact electronicproduct, Semiconductor Mounting Technology (SMT) is widely used, and apackaging technology of the semiconductor device employs a technologyfor minimizing an installation space such as a Ball Grid Array (BGA), awire bonding, and a flip chip bonding.

FIG. 1 is a view illustrating a process for fabricating a light emittingdiode according to the related art.

As shown in FIG. 1, a gallium nitride (GaN) buffer layer 101 is formedon a sapphire substrate 100 formed of Al₂O₃. After that, a GaN layer103, which is not doped with dopants (Hereinafter, referred to as“undoped”), is formed on the GaN buffer layer 101.

In order to form a Group 3-based element in a form of a thin film on thesapphire substrate 100 as described above, a metal organic chemicalvapor deposition (MOCVD) is generally used. At this time, the thin filmlayer is formed under a constant growth pressure.

An N-type GaN layer 105 is formed on the undoped GaN layer 103, andsilicon using silane (SiH₄) or disilane (Si₂H₆) gases is used to formthe N-type GaN layer 105.

After the N-type GaN layer 105 is formed, an active layer 109 is formedon the N-type GaN layer 105. The active layer 109 functioning as a lightemission region is a semiconductor layer having an illuminant formed ofa indium gallium nitride(InGaN).

After the active layer 109 is formed, a P-type GaN layer 110 issubsequently formed.

The P-type GaN layer 110 is in a contrast to the N-type GaN layer 105.Namely, electrons are drifted by an external voltage in the N-type GaNlayer 105, while holes are drifted by the external voltage in the P-typeGaN layer 110. Therefore, the holes and the electrons are mutuallyrecombined in the active layer 109, thereby emitting light.

A transparent metal (TM) layer using a transparent Indium-Tin-Oxide(ITO) metal is formed on the P-type GaN layer 110 so that lightgenerated at the active layer 109 is transmitted and emitted to theexternal.

After the TM layer is formed, a P-type electrode is formed to completethe LED.

However, the LED constructed as above has a drawback in that a strain isincreased due to an inconsistency of the lattice constants between theInGaN layer of the active layer and the GaN layer, thereby reducing anamount of light generated in the active layer.

Further, the inconsistency of the lattice constant deteriorates aproduct reliability of the LED. Also, there is a drawback in that theactive layer, which is formed on the N-type GaN layer adjacent to theactive layer in a form of a two-dimensional plane, has a lower luminousintensity than a three-dimensional formation.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is directed to an LED and afabrication method thereof that substantially obviate one or moreproblems due to limitations and disadvantages of the related art.

An object of the present invention is to provide an LED and afabrication method thereof in which a GaN layer having a lowconcentration of indium (In) is formed between the active layer and anN-type GaN layer to reduce an inconsistency of lattice constants betweenan active layer and a GaN layer, thereby increasing a light efficiencyand improving a product reliability.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a lightemitting diode includes: a buffer layer disposed on a sapphiresubstrate; a GaN layer disposed on the buffer layer; an N-type GaN layerdisposed on the GaN layer; a GaN layer having indium disposed on theN-type GaN layer; an active layer disposed on the GaN layer havingindium; and a P-type GaN layer disposed on the active layer.

Here, an empirical formula of the GaN layer having indium is given byIn(x)Ga(1-x)N and a range of x is given by 0<x<2, and a thickness of theGaN layer having indium is 50-200 Å.

Also, a GaN layer whose thickness is 10-30 Å is formed on the GaN layerhaving indium, and the active layer is of a multi-quantum well structurehaving a InGaN/GaN structure.

Also, a method for fabricating a LED according to the present invention,includes the steps of: forming a buffer layer on a sapphire substrate;forming a GaN layer on the buffer layer; forming an N-type GaN layer onthe GaN layer; forming a GaN layer having indium on the N-type GaNlayer; forming an active layer on the GaN layer having indium; andforming a P-type GaN layer on the active layer.

Here, after the GaN layer having indium is formed, a GaN layer issubsequently formed at a thickness of 10-30 Å, and the active layer isformed in 1 period to 7 periods under a temperature condition of600-800° C.

Also, after the active layer is formed, the P-type GaN layer is formedat a thickness of 750-1500 Å at a temperature of 980-1020° C.

According to the present invention, the InGaN layer having a lowconcentration of indium is formed between the N-type GaN layer and theactive layer formed on the sapphire substrate, so that deterioration oflight efficiency due to inconsistency of a lattice constant between theGaN layer and the active layer is prevented and the light efficiency canbe improved.

Also, the InGaN layer having a low Indium composition has a threedimensional structure on its surface and such three-dimensional growthof the surface can improve the light efficiency even more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a process for fabricating an LED accordingto the related art;

FIGS. 2 a through 2 d are views illustrating a process for fabricatingan LED according to the present invention; and

FIG. 3 is a view schematically showing a P-type GaN layer formedaccording to a quantum well growing method among the method forfabricating the LED according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to accompanying drawings.

FIGS. 2 a through 2 d are views illustrating a process for fabricating alight emitting diode (LED) according to the present invention.

As shown in FIGS. 2 a through 2 d, a buffer layer 201 having anempirical formula of In(x)Ga(1-x)N is formed on a sapphire (Al₂O₃)substrate 200 at a temperature of 500-600° C., and an undoped GaN layer203 is grown up to a thickness of 1-3μm on the buffer layer 201 at atemperature of 1000-1100° C. (FIG. 2 a).

Next, an N-type GaN layer 205 is grown up to a thickness of 1-3μm on theundoped GaN layer 203 at a temperature of 1000-1100° C. (FIG. 2 b).

After the N-type GaN layer 205 is formed, a GaN layer 207 having a lowmole of indium (In) is grown up at a temperature of 600-800° C. beforean active layer 209 is formed (FIG. 2 c).

The composition ratio of indium in the InGaN layer 207 is given byIn(x)Ga(1-x)N(0<x<0.2). The In(x)Ga(1-x) N(0<x<0.2) layer is grown up toa thickness of 50-200 Å.

After the InGaN layer 207 is formed, an active layer 209 is formed.

The active layer 209 is formed of GaN layer at a thickness of 10-30 Åand makes an electron tunnels into a quantum-well layer, therebypreventing holes from penetrating into the In(x)Ga(1-x)N(0<x<0.2) layer.

The active layer 209 of the InGaN/GaN having a multi-quantum-wellstructure is formed in 1 period to 7 periods at a temperature of600-800° C.

After the active layer 209 is formed, a P-type GaN layer 210 doped witha dopant of magnesium (Mg) is formed grown up to a thickness of 750-1500Å at a temperature of 980-1020° C.

FIG. 3 is a view schematically showing a P-type GaN layer formedaccording to a quantum-well growing method among the method forfabricating the LED according to the present invention.

As shown in FIG. 3, in the quantum-well growing method, a well growingstep of forming a well layer 301 that includes various dopants such asIn, Ga, and N is performed. Here, a growth condition of the well layer301 is given by TMGa: 0-200μ mol/min, TMIn: 0-100 μ mol/min, NH₃: 0-80L/min, growing temperature 600-800° C.

Subsequently, an enough crystal time is given so that the dopantsincluded in the step of growing the well layer 301 may combine eachother completely to form a crystal layer 302, whereby a combiningability of In and N, Ga and N, In and Ga inside the well layer 301, isimproved.

Here, a growth time of the crystal layer 302 is given by 0.1 sec -60 minand N₂: 30-50 L/min, H₂: 30-50 L/min.

Next, a barrier growing step of forming a barrier layer 303 includingvarious dopants such as Ga, N, is performed. Here, a growth condition ofthe barrier layer 303 is given by TMGa: 100-500 μ mol/min, TMIn: 50-200μ mol/min , NH₃: 0-80 L/min, growing temperature: 600-800° C.

As described above, the active layer 209 is formed so as to have amulti-quantum well structure in the present invention, and the GaN layer207 having the low concentration of indium is formed in a shallowthickness on the N-type GaN layer 205 at a low temperature, so thatinconsistency of the lattice constant with the active layer 209 isreduced and light efficiency can be improved.

Also, since the InGaN layer of the active layer 209 is formed through athree-dimensional growth, a brightness of light generated at the activelayer 209 is increased.

INDUSTRIAL APPLICABILITY

As described above in detail, the present invention forms the InGaNlayer having a low concentration of indium between the N-type GaN layerand the active layer formed on the sapphire substrate, thereby reducinginconsistency of the lattice constant with the active layer andimproving light efficiency.

Further, the InGaN layer having the low concentration of indium, has athree dimensional structure on its surface, and light efficiency can beimproved even more in case a surface has such a three-dimensionalstructure.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

1. A method for fabricating an LED (light emitting diode), comprising:forming an N-type GaN layer; forming a GaN layer having indium above theN-type GaN layer, wherein a thickness of the GaN layer having indium is50-200 Å; forming an active layer above the GaN layer having indium; andforming a P-type GaN layer above the active layer.
 2. The methodaccording to claim 1, wherein the GaN having indium is formed at atemperature of 600-800° C.
 3. The method according to claim 1, whereinafter the GaN layer containing indium is formed, a GaN layer is formedat a thickness of 10-30 Å.
 4. The method according to claim 1, whereinthe active layer is formed in 1 period to 7 periods under a temperaturecondition of 600-800° C.
 5. The method according to claim 1, whereinafter the active layer is formed, the P-type GaN layer is formed at athickness of 750-1500 Å under a temperature condition of 980-1020° C. 6.The method according to claim 1, wherein the step of forming the activelayer includes forming a well layer, forming a crystal layer, andforming a barrier layer.
 7. The method according to claim 6, wherein agrowth condition of the well layer is given by TMGa: 0-200 μmol/min,TMIn: 0-100 μmol/min, NH₃: 0-80 L/min, growing temperature: 600-800° C.8. The method according to claim 6, wherein a growth condition of thecrystal layer is given by a growth time of 0.1 sec-60 min and N₂: 30-50L/min, H₂: 30-50 L/min.
 9. The method according to claim 6, wherein agrowth condition of the barrier layer is given by TMGa: 100-500μmol/min, TMIn: 50-200 μmol/min , NH₃: 0-80 L/min, growing temperature:600-800° C.
 10. A method for fabricating an LED (light emitting diode),comprising: forming an N-type GaN layer; forming a GaN layer havingindium above the N-type GaN layer; forming a GaN layer above the GaNlayer having indium; forming an active layer directly on the GaN layer;and forming a P-type GaN layer above the active layer.
 11. The methodaccording to claim 10, wherein the GaN having indium is formed at atemperature of 600-800° C.
 12. The method according to claim 10, whereina thickness of the GaN layer is 10-30 Å.
 13. The method according toclaim 10, wherein the active layer is formed in 1 period to 7 periodsunder a temperature condition of 600-800° C.
 14. The method according toclaim 10, wherein the P-type GaN layer is formed at a thickness of750-1500 Å under a temperature condition of 980-1020° C.
 15. The methodaccording to claim 10, wherein the GaN layer is directly formed on theGaN layer having indium.
 16. The method according to claim 10, whereinthe step of forming the active layer includes forming a well layer,forming a crystal layer, and forming a barrier layer.
 17. The methodaccording to claim 16, wherein a growth condition of the well layer isgiven by TMGa: 0-200 μmol/min, TMIn: 0-100 μmol/min, NH₃: 0-80 L/min,growing temperature: 600-800° C.
 18. The method according to claim 16,wherein a growth condition of the crystal layer is given by a growthtime of 0.1 sec-60 min and N₂: 30-50 L/min, H₂: 30-50 L/min
 19. Themethod according to claim 16, wherein a growth condition of the barrierlayer is given by TMGa: 100-500 μmol/min, TMIn: 50-200 μmol/min , NH₃:0-80 L/min, growing temperature: 600-800° C.